The grass genera of the world
Including Plagiarthron Duv.
Habit, vegetative morphology. Perennial; caespitose. Culms 100 cm high; herbaceous; unbranched above. Culm nodes glabrous. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; without cross venation. Ligule an unfringed membrane; 0.8–1 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic (the pedicellate spikelet sometimes reduced to its glumes), or homomorphic; all in heterogamous combinations.
Inflorescence. Inflorescence a single apical raceme. Rachides hollowed, or flattened. Inflorescence espatheate (seemingly); not comprising partial inflorescences and foliar organs. Spikelet-bearing axes spikelike (erect, subcylindrical); solitary; with substantial rachides; disarticulating; disarticulating at the joints. Articles non-linear (hollowed to receive the sessile spikelet); appendaged; disarticulating obliquely; densely long-hairy. Spikelets paired; not secund; sessile and pedicellate (the pedicels resembling the internodes); consistently in long-and-short combinations; in pedicellate/sessile combinations. Pedicels of the pedicellate spikelets free of the rachis. The shorter spikelets hermaphrodite. The longer spikelets hermaphrodite, or male-only, or sterile.
Female-sterile spikelets. The pedicelled spikelet well developed to much reduced, its lower glume sometimes attenuate into a long, curved awn.
Female-fertile spikelets. Spikelets 7.5 mm long; compressed dorsiventrally; falling with the glumes (attached to the joint and pedicel). Rachilla terminated by a female-fertile floret. Hairy callus present (the hairs encircling each node). Callus short (and broad); blunt.
Glumes two; more or less equal; long relative to the adjacent lemmas; hairy; without conspicuous tufts or rows of hairs; awnless; very dissimilar (G1 leathery and keel-less, G2 thinner and boat-shaped). Lower glume not two-keeled (seemingly); convex on the back to flattened on the back; not pitted; 7–9 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate; male. The proximal lemmas awnless; 3(–5) nerved; decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (thinly membranous); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (thinly membranous); not becoming indurated; entire; pointed, or blunt; awnless; hairless; non-carinate; without a germination flap; 3 nerved. Palea present; relatively long; entire; awnless, without apical setae; not indurated; 2-nerved. Lodicules present; 2; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles fused. Stigmas 2.
Fruit, embryo and seedling. Hilum short. Pericarp unknown in mature state.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (in L. ledermannii), or absent; intercostal. Intercostal papillae over-arching the stomata (conspicuously, at one end); consisting of one oblique swelling per cell (at one end of each interstomatal). Intercostal zones with typical long-cells (in L. caespitosa), or exhibiting many atypical long-cells (in L. ledermannii, where perturbation is associated with the basal rosettes of abundant macrohairs). Mid-intercostal long-cells rectangular (irregularly so in L. ledermannii); having markedly sinuous walls to having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; panicoid-type; (33–)40–62(–69) microns long; 8.4–11.4 microns wide at the septum. Microhair total length/width at septum 2.9–5.4 (L. ledermanni), or 5.1–7.2 (L. caespitosa). Microhair apical cells (19.5–)22–30(–33) microns long. Microhair apical cell/total length ratio 0.47–0.59. Stomata common; 30–36 microns long (L. ledermanni), or 36.6–40.5 microns long (L. caespitosa). Subsidiaries non-papillate; predominantly triangular (often with truncated apices, in L. caespitosa). Guard-cells overlapped by the interstomatals (slightly), or overlapping to flush with the interstomatals. Intercostal short-cells common (solitary, associated with prickle bases, in L. caespitosa), or absent or very rare. Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired (the arrangement varying from place to place in both species seen). Costal silica bodies panicoid-type; short, dumb-bell shaped, or cross shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath outlines even. PCR sheath extensions absent. Mesophyll traversed by columns of colourless mesophyll cells (occasionally, from colourless arches), or not traversed by colourless columns. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (the large median flanked on either side by several smaller bundles, and with large laterals at the outer margins of the midrib zone); with colourless mesophyll adaxially (comprising two large bulliform groups, and a mass of underlying colourless tissue contiguous with them which extends across the blade). The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (between pairs of main bundles); in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (with colourless masses formed from bulliforms and contiguous underlying colourless tissue occupying the adaxial part of the blade between each pair of main bundles); associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with all the main laterals); forming figures (mostly slender Ts or Is). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 3 species.
Distribution, phytogeography, ecology. Tropical southern Africa.
Helophytic; glycophytic. Savanna, in damp drainage hollows.
References, etc. Morphological/taxonomic: Launert 1961, 1963, 1965a; Clayton 1977. Leaf anatomical: this project.
Special comments. Fruit data wanting.
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 13th November 2017. delta-intkey.com/grass’.